The present commercial method is air roasting. The production of SO.sub.2 is controlled by the Environmental Protection Agency. The SO.sub.2 produced by any roasting of sulfides requires the addition of scrubbers and perhaps the construction of a sulfuric acid plant.
A laboratory method for digestion of MoS.sub.2 is oxidation with HNO.sub.3. However, this also causes pollution problems with the NO.sub.x vapors which are produced. Again, there is no inexpensive way of removing these vapors.
Digestion of MoS.sub.2 in boiling H.sub.2 SO.sub.4 is also possible; however, this requires excessive amounts of H.sub.2 SO.sub.4 (1 gram of MoS.sub.2 to 10 grams of H.sub.2 SO.sub.4). Also, a temperature of 240.degree. C. for 5 hours is necessary. During this boiling period, SO.sub.3 vapors are coming off and must be scrubbed.